The present invention relates to an electrode, especially for examinations by electrocardiography (ECG), of the type that is fastened to the patient's skin by vacuum generated in a cup-like chamber pressed against the skin.
In practice, two main types of electrodes are used at present. On one hand there are disposable electrodes which are fastened by adhesive means (adhesive paste, tape, etc.) or with rubber bands and the like. On the other hand there are multiple-use electrodes working with locally generated vacuum. An old vacuum-based fastening principle uses compressed and thereafter expanding (squeezable) rubber balls, which, however, because of the limited reservoir size are prone to come loose even if there is only the slightest leakage and which, therefore, give rise to appreciable difficulties, e.g., if there are six electrodes to be used simultaneously with a single patient, as is common in clinical routine. None of these systems is thus completely satisfactory.
An electrode that is attached with the aid of vacuum supplied via a flexible tube, and where a valve for this vacuum is closed when the electrode is not attached, opening automatically on application and closing automatically if the electrode comes loose and falls off, is known from Austrian Patent Specification No. 248 608. According to a particular embodiment described in that patent, a spring-loaded electrode plate is connected to a sealing ring by way of an elastic membrane. When the electrode plate is pressed against the skin of a patient, a valve opens and vacuum is generated in a chamber around the electrode, this chamber being defined by the sealing ring. Unfortunately, the movability of the electrode plate in relation to the sealing ring via a membrane can result in a bad fit of the electrode to the skin because the electrode plate can both tilt and move axially relative to the sealing ring by means of the elastic membrane, unless high negative pressures of the sort leaving marks on the skin are used. There is, furthermore, no guarantee for the pressure of the electrode on the skin to be constant, causing the proper electrical functioning of the electrode to be dependent on the patient being at rest. Very small movements of the electrode are accompanied by changes in contact resistance, causing the baseline against which the ECG-variable is recorded to lack in definition and to become variable. The fixation by vacuum with a single vacuum source for many electrodes, although being advantageous from a theoretical standpoint, for practical purposes has, therefore, not come into common use.
An electrode which is kept in place by vacuum and which has a surrounding sealing ring connected in a relatively rigid way to a centrally located electrode plate is known from U.S. Pat. No. 4,248,243. This electrode cannot, however, be kept under vacuum by connection to a central vacuum source, because it is lacking the self-closing valve described in the above-referred to Austrian patent specification. The electrode of U.S. Pat. No. 4,248,243 is fed with pressurized air, which drives an ejector pumping device mounted in the electrode. This means that the electrode is very disturbing to a patient during examination, because the ejector device makes a hissing or whizzing sound. Moreover, material from the electrode vacuum chamber is blown into the air through the ejector nozzle, such material including constituents of the electrode paste used with the electrode and non-sterile body fluids formed by sweating, which thus gives rise to sanitary problems. Because of its specific design, this electrode can be sterilized only with difficulty, and it is impractical to use it as a disposable electrode. It is further to be noted that relatively high positive pressures have to be supplied, about 0.6 kg per cm.sup.2, causing greater sealing difficulties and requiring the use of pressure hose.